The present invention relates to a data processing technique for storing a copy of data.
As represented by a remote copy function used between storage systems, a data backup system using a main site information processing system (also referred to as “primary system”) and a sub site information processing system (also referred to as “secondary system”) is adopted widely in the field of disaster measures, etc. The main site information processing system and the sub site information processing system form a duplication system and have disk array devices (first and second storage devices) respectively so that data or backup data are stored in a database for each disk array device while separated by logical volumes. That is, logical volumes (first logical volumes) in which data in the main site information processing system are stored are paired with logical volumes (second logical volumes) in which backup data in the sub site information processing system are stored, so that the first logical volumes correspond to the second logical volumes respectively. A log transfer method as disclosed in JP-A-2002-259183 is used as a data backup method using such a duplication system.
The log transfer method is a method in which a data update record (hereinafter referred to as “log”) in the main site information processing system is transferred to the sub site information processing system so that backup data is generated in the sub site information processing system. In the log transfer method, data in the main site information processing system and backup data in the sub site information processing system are first synchronized (mirrored) with each other at the stage of the start of a backup process. When the backup process starts, the log stored in a logical volume in the main site information processing system is transferred to the sub site information processing system. In the sub site information processing system, while the transferred log is copied into a logical volume paired with the logical volume of the main site information processing system, the newest backup data are generated on the basis of the copy of the log and stored in a logical volume of the database.
Incidentally, if a line failure occurs in the middle of data transfer between the main site information processing system and the sub site information processing system when the log transfer method is used for backing up data, the pair state between logical volumes in which the log is stored is suspended. In this case, data updating is executed only for the logical volumes of the main site information processing system, that is, data updating is not executed for the logical volumes of the sub site information processing system. Accordingly, when the line in a failure state is recovered, re-synchronization must be performed to attain recovery of the backup state in the duplication system.
To secure reliability of the duplication system in the re-synchronization at the time of recovery of the line, it is necessary to give a guarantee that the logical volumes in the sub site information processing system are prevented from being updated during the occurrence of the line failure.